On Wed, 30 Jan 2019 at 3:48 PM, Steven D'Aprano steve@pearwood.info wrote:

This thought is motivated by this bug report:

https://bugs.python.org/issue35857

If you import a module, then edit the .py file that goes with it, and then an exception occurs, the stack trace can show the wrong line.

It doesn't happen very often, but when it does happen, it can be very perplexing. Here's a proposal:

When a stack trace is printed, before printing each line, the interpreter checks whether the file's modification time is later than the time recorded in the .pyc file. If the times are different, the stack trace can flag the line and print an addition line stating that the file may have changed and the stack trace may not be accurate.

Something like this perhaps?

Traceback (most recent call last): File "spam.py", line 99, in <spam> eggs.foo() File "eggs.py", line 123, in <eggs> ? for obj in sequence: File "cheese.py", line 456, in <cheese> n = len(x) *** one or more files may have changed *** lines starting with ? may be inaccurate TypeError: object of type 'NoneType' has no len()

I don't think performance will matter. Generating stack traces are rarely performance critical, so I don't think that a few extra file system checks will make any meaningful difference.

Thoughts?

I like this idea. A variation would be to just add " (modified)" to the file name - line number bits of the stack trace, for the appropriate files.

-- Pradyun

-- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/

I've been bitten by this and it always costs me several minutes of confusion.

+1

On 30 Jan 2019, at 11:17, Steven D'Aprano steve@pearwood.info wrote:

This thought is motivated by this bug report:

https://bugs.python.org/issue35857

If you import a module, then edit the .py file that goes with it, and then an exception occurs, the stack trace can show the wrong line.

It doesn't happen very often, but when it does happen, it can be very perplexing. Here's a proposal:

When a stack trace is printed, before printing each line, the interpreter checks whether the file's modification time is later than the time recorded in the .pyc file. If the times are different, the stack trace can flag the line and print an addition line stating that the file may have changed and the stack trace may not be accurate.

Something like this perhaps?

Traceback (most recent call last): File "spam.py", line 99, in <spam> eggs.foo() File "eggs.py", line 123, in <eggs> ? for obj in sequence: File "cheese.py", line 456, in <cheese> n = len(x) *** one or more files may have changed *** lines starting with ? may be inaccurate TypeError: object of type 'NoneType' has no len()

I don't think performance will matter. Generating stack traces are rarely performance critical, so I don't think that a few extra file system checks will make any meaningful difference.

Thoughts?

-- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/

On Wed, 30 Jan 2019 at 16:34, Alex Walters tritium-list@sdamon.com wrote:

...

-----Original Message----- From: Python-ideas <python-ideas-bounces+tritium- list=sdamon.com@python.org> On Behalf Of Jonathan Fine Sent: Wednesday, January 30, 2019 6:40 AM To: python-ideas python-ideas@python.org Subject: Re: [Python-ideas] Stack traces ought to flag when a module has been changed on disk

I think Steve's suggestion fails in this situation. Suppose wibble.py contains a function fn. Now do import wibble fn = wibble.fn # Modify and save wibble.py reload(wibble) fn()

I think using reload should raise warnings, since it doesn't work, and the reload case shouldn't be the killer of this really good idea.

Reload isn't the issue here. Even without the reload the call to `fun()` will no longer match the file on disk.

reload was moved to the imp module for exactly that reason.

Michael

...

I've posted a message to this effect in the original bug https://bugs.python.org/msg334553

Please note that the original poster, after the cause has been explained, is happy for the bug to be closed. https://bugs.python.org/msg334551

Perhaps move discussion back to https://bugs.python.org/issue35857.

Jonathan _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/

---

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On Wed, Jan 30, 2019 at 3:43 AM Jonathan Fine jfine2358@gmail.com wrote:

I think Steve's suggestion fails in this situation. Suppose wibble.py contains a function fn. Now do import wibble fn = wibble.fn # Modify and save wibble.py reload(wibble) fn()

Sure -- but this is just a warning that there *might* be an issue -- if a user doesn't get the warning in some cases (particularly cases in which they have used an "advanced" feature like reload) we aren't any worse off.

+1 on the idea -- I don't see a downside.

-CHB